1. Field of the Invention
The present invention generally relates to recycling of metal-containing sludge and, more particularly, to a method of and an apparatus for realizing a recycle of a grinding sludge by compressing a grinding sludge of hardened component parts produced in a grinding line, for example, ferrous component parts of rolling bearings such as inner and outer races and rolling elements or any other grinding sludge, to thereby form a compressed material (hereinafter referred to as a “briquette”) and also to the compressed material and a recycling system therefore.
2. Description of the Prior Art
Ferrous component parts of rolling bearings such as inner and outer races and rolling elements are, after having been hardened, subjected to a grinding process to grind raceways and others. Powdery grinding scraps or ground chips produced as a result of the grinding are discharged as a sludge together with a coolant to the outside of the system and are then filtered so that the coolant can be reused. The grinding sludge left as a result of the filtration is in most cases buried in landfill.
FIG. 19 illustrates a block diagram showing the flow of the process. The grinding scraps produced by a grinding machine 101 is fed together with a coolant through a piping and is then filtered by a filtering means such as a filter or a settling equipment 102, with the filtered coolant being returned by a pump by way of a filter back to a coolant reservoir 103 from which the coolant is supplied to the grinding machine 101. The grinding sludge left after filtration still contains a quantity of the coolant, wherefore it cannot be reused and, hence, is disposed by an industrial waste material disposing industry as, for example, land filling.
Although the amount of the grinding scraps produced as a result of the grinding is relatively small as compared with the amount of cutting scraps, a mass-production line for manufacture of, for example, bearings results in a relatively large quantity of the grinding scraps and, not only is the burying of the grinding sludge in landfill generally considered undesirable from the standpoint of environmental pollution, but also it is obvious that in view of the waste treatment sites reaching an dead end, the grinding sludge would no longer be buried in landfill.
Under these circumstances, it has been suggested to compress the grinding sludge by squeezing to provide a compressed material (referred hereinafter to as a “briquette”) so that the coolant squeezed therefrom can be reused while the briquette can be used as a material for steel production.
The grinding sludge using a water-based coolant can easily be compressed to provide the briquette and, in fact, a compressing machine therefore is being sold in the market.
Unfortunately, an oil-based coolant has a higher viscosity than that of the water-based coolant and, therefore, the grinding sludge using the oil-based coolant provides various problems in compressing it. By way of example, during squeezing the oil-based coolant is difficult to be drained and even though the pressure used during squeezing is increased, compression of the grinding sludge to a required strength cannot be achieved. For this reason, compression of the grinding sludge containing the oil-based coolant has not yet been practiced.
In a grinding line in which in the course of manufacture of rolled steel plates, grinding is carried out to remove flaws appearing on surfaces of metal plates, it has been suggested to filter a grinding sludge and then compress it by squeezing to thereby recover a compressed material as a briquette so that the briquette can be reused as material for production of the rolled steel plates. The grinding sludge produced as a result of grinding of the rolled steel plates contains grinding scraps that are so soft and pliable as to allow the grinding sludge to be easily compressed. Also, the grinding sludge so produced has a relatively small quantity of coolant, allowing such grinding sludge to be easily compressed.
In contract, in the case of the grinding sludge produced from hardened component parts, the grinding sludge is hard and difficult to turn into a solid. For this reason, the grinding sludge from the hardened component parts have to be strongly compressed. Unfortunately, the grinding sludge containing the oil-based coolant as hereinbefore described is more difficult to be turned into a solid since difficulty is often encountered in draining the coolant during squeezing. Also, in the case of the grinding sludge from the hardened component parts, since a few tens of milliliter per minute of the coolant is used for grinding, for example, 1 to 2 grams of steel, the proportion of the coolant in the grinding sludge is relatively high and, considering that a major portion of the grinding sludge is occupied by the coolant, such grinding sludge is hard to be turned into a solid.
The briquette formed by compressing a grinding powder and the briquette formed by compressing the grinding sludge containing the water-based coolant, both hitherto available, generally represents a cylindrical shape as shown in FIG. 18. However, in order for the oil-based coolant having a relatively high viscosity to be efficiently squeezed, it is considered feasible to increase the inner and outer circumferences of the briquette B without the applied surface pressure during a press work being reduced. The use of a drain passage for drainage of an oil component or a pressure valve in a punch for squeezing the grinding sludge has been suggested, but there is a high risk of the sludge clogging in the drain passage or the pressure valve and, therefore, the suggested use of the drain passage and the valve is not practical.